sedimentary
Quartz Geode
Crystalline Silicon Dioxide (SiO2) in sedimentary matrix
Hardness: 7 on Mohs scale; Color: Tan to white exterior, likely clear/white interior; Luster: Dull/earthy exterior, vitreous interior; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Tan to white exterior, likely clear/white interior
- Luster
- Dull/earthy exterior, vitreous interior
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to white exterior, likely clear/white interior; Luster: Dull/earthy exterior, vitreous interior; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed primarily in sedimentary rocks like limestone or volcanic ash beds where mineral-rich groundwater precipitates silica into cavities or bubbles over thousands of years.
Uses & applications
Primarily used as decorative specimens, for education, and by collectors. Larger amethyst-filled geodes are used in high-end decor.
Geological facts
Geodes are like nature's 'jackpots'; from the outside they look like ordinary lumpy rocks, but the inside can contain spectacular crystal cathedrals.
Field identification & locations
Identify in the field by their rounded, lumpy, cauliflower-like exterior and unusually light weight for their size. Commonly found in desert regions of the US, Mexico, and Brazil.
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